Various single and dual spring arm female contact electrical terminals have been provided in the past for making electrical contact with male terminals such as pins, blades, edge card contact pads and the like. In order to establish satisfactory electrical connection, one of the terminals must exert sufficient pressure on the other resulting in a minimum contact normal force being exerted when the terminals are in a final mated position. However, this pressure causes frictional drag during insertion and removal, therefore, the male terminal must be inserted into the female terminal with sufficient force to overcome the resistance to insertion presented by the female terminal. In addition, the insertion force of the contact structure must include a lifting component which represents the force required to lift or spread the female contact portions apart to permit insertion of the male terminal into the female terminal as well as the horizontal frictional component which is a result of the female contact portions wiping against the male terminal during the insertion. As a result, in multicircuit arrangements including a large number of female terminals mounted in a connector adapted to mate with a male connector having a correspondingly large number of male terminals, the individual insertion forces associated with each pair of terminals combine so that the overall insertion force required to mate the male and female connectors may be extremely high.
Earlier efforts to provide an electrical contact structure characterized by reduced insertion force have generally included modifying the female terminal or contacts. In U.S. Pat. No. 4,175,821, for example, a female terminal is disclosed which includes a dual opposed spring arm contact member wherein the contact portions of the opposed arms are axially offset from one another in the longitudinal direction. As a male pin contact is inserted between the female spring arms, the pin engages the first spring arm on the female terminal and lifts it out of the way, before contacting the second spring arm and moving that contact out of the way. As a result, a lower peak insertion force is achieved because the male terminal lifts only one female spring arm at a time.
Another modified low insertion force female terminal is disclosed in U.S. Pat. No. 4,607,907. The female contact in this patent is a stamped and formed terminal which includes a rearward box-like member from which extend cantilevered spring arms having contact portions at their free ends. The contact portions are axially longitudinally offset similar to the contact portions in the aforementioned patent, but, in addition, they are configured so that they overshoot the midline of the insertion region which permits lower spring rates to be used, both factors of which contribute to an overall low insertion force female terminal.
Subsequent efforts to provide an electrical contact structure characterized by reduced insertion force have included modifying the male terminal contacts. For instance, in U.S. Pat. No. 4,740,180, dated Apr. 26, 1988 and assigned to the assignee of this invention, a low insertion force contact structure is disclosed including a male terminal having a twisted lead-in portion with at least one surface adapted to engage at least one contact of a female terminal. Specifically, during insertion the twisted lead-in portion of the male terminal is effective to gradually cam outwardly contact portions of a pair of spring arms of the female terminal from an initial position to a final mated position to provide a low overall insertion force and at the same time provide a high contact normal force between the female and male terminals. The mating electrical contact structure and camming profile disclosed in this patent have proven effective to provide a highly reliable, low insertion force contact interface. However, the design is not easily adaptable for miniaturization beyond a certain point, i.e. for reducing individual terminal size in order to produce denser arrays of terminals in increasingly smaller packages. Furthermore, the solid lead-in portion of the male terminal has limited mating depth and does not generally permit applications in which sequential or staggered mating may be required. Although these limitations are not critical in many applications, they may provide potential problems in some specific connector applications.
Therefore, the present invention is directed to further improvements in electrical contact structures characterized by reduced insertion forces, particularly of the type shown in U.S. Pat. No. 4,740,180.